As if turning 30 was not enough of a worry for some, psychologists have discovered that the milestone also marks the end of a decade in which people often make their most cherished memories.

Chris Moulin, from the University of Leeds, told the festival that a study of a group of middle-aged and older people had uncovered a "reminis cence bump", rich in memories between the ages of 20 and 30.

"We've been exploring this idea because this is supposed to be a time in your life when it's crucial for laying down yourself; in some ways becoming yourself," said Dr Moulin.

Eighteen people in their 50s and 60s were asked to recall memories that associated with neutral words such as restaurant or train.

"If you give them a free rein to do those sorts of things, they have a marked tendency to generate memories from a time in which they were in their 20s," said Dr Moulin.

One reason could be that lots of exciting, life-changing things often happen in a person's 20s. "You get your qualifications, you get a life partner and so on," he said. "The task of psychologists is to disentangle that explanation from a more scientific idea to do with the self. The reminiscence bump could just be that it's when the most exciting things happen in your life. What we'd like to argue is that it's to do with the formation of the self."

Another theory in that the frontal lobes of the brain, where much of the higher intelligence functions are controlled, do not develop fully until the end of puberty.

"The frontal lobes are the last part of the brain to develop. They are critical in the formation of self and in the organisation of memory."